It’s set in the 1970s, but it has such urgent resonance for the world in 2017 that it’s almost disturbing to watch. The depiction of rotten relationships – on a geo-political and on a personal level – catches you up so that sometimes it’s hard to stomach the fabulous entertainment.

And there’s lots of entertainment, because this is Miss Saigon, and Cameron Mackintosh’s production of Boublil and Schonberg’s blockbuster musical is a magnificent production. A rework of Madame Butterfly first produced in London in 1989, it has stormed Broadway and the West End since then.

Epic in scale, execution and skill, it is presented as a “tragic love story”, set during the confusion as the Americans are about to pull out of Vietnam in April 1975. Kim (Sooha Kim) is a demure, virginal 17-year-old Vietnamese villager forced into prostitution by monstrous French Vietnamese pimp The Engineer (Red Concepcion).

She and American GI Chris (Ashley Gilmour) fall in love after her first night on the job and marry. They are separated in the melee of US withdrawal, and a few years later it all comes home to roost; Chris is home in the US with his new American wife, Kim is living in a shantytown in Vietnam with their three year old son, dreaming of her lost husband.

The cast give wonderfully strong performances (particularly Sooha Kim and Red Concepcion), and the set is magnificent. The action spans continents and emotions, and if the songs are not all hummable, even after almost 30 years, they are forthright and bold and excellently executed.

But it is the operatic production that stuns, particularly the deservedly famed setpieces: the helicopter arrival at the US embassy for the chaotic exit, the Engineer’s grotesque ode to America, all slavering and shimmying, in The American Dream, the post-war Communist dragon and army spectacle.

This is almost flawless showbiz. No wonder it’s such a hit. And yet.

The subject matter here is not a romantic love story. It is full of human desperation, exploitation, degradation, lines of refugees, western sex tourism, set against a background of international aggression, the sale of human flesh and the ostracising of the children who are the detritus of US soldiers.

The initial romance is unlikely and unbelievable and predicated on a heartbreaking imbalance of power. The brothel scenes in the ironically named Dream Land are horrible but do they lean towards titillation as well as seediness and coercion? There’s more than a shade of the dodgy Officer and a Gentleman about this; only this time the prostitute who is saved is meek, Asian, and dies.

Saigon has been criticised for perpetuating colonial assumptions and racial stereotypes (Asian women as passive, sexual playthings, Asian men as loathsome and evil); but the argument against that is: this is what happened during the Vietnam war. Les Mis, from the same writers and producer, is also gritty; perhaps this is more uncomfortable because exploitation of the disenfranchised, US aggression, the desperation of refugees, are still a reality worldwide.

This is a stunning show, make no mistake, and if it’s sometimes hard to stomach the intersection of showbiz and the brutality of what it has turned into glitzy entertainment, it still makes for breathtaking stagecraft, a rousing night, and enormous audience pleasure.